A single-cylinder plug pin system is a device built in a crane boom for achieving a telescopic function of the crane boom which mainly comprises telescopic arms and a telescopic oil cylinder. The single-cylinder plug pin system includes arm pins, arm pin holes, a cylinder head, cylinder pins, a cylinder rod, a cylinder barrel, a dovetail groove, detection switches and other auxiliary facilities and is a main functional assembly for achieving extension and retraction of a lifting arm. The cylinder head is a device, which is located at a certain position of the cylinder barrel or the piston rod of the telescopic oil cylinder and is adopted to control fixation and separation of the telescopic oil cylinder and the telescopic arms, and the cylinder head mainly includes an arm pin driving device, cylinder pins, a driving oil cylinder, a position detection block, etc. The cylinder pin is a pin on the cylinder head of the telescopic oil cylinder and is adopted to lock the telescopic oil cylinder with the telescopic arms, and each cylinder head in an existing product generally includes 2 or 4 cylinder pins. The arm pin is a pin on the telescopic arm and is adopted to lock various telescopic arms, and each telescopic arm in the existing product generally includes 1 or 2 arm pins. The arm pin driving device is a device adopted to pull down or push up the arm pins and to lock or unlock the telescopic arms. The detection switches are sensors adopted to detect the arm positions of the telescopic arms and the locking and unlocking states of the cylinder pins or the arm pins.
FIG. 1a shows a single-cylinder plug pin type telescopic arm, this telescopic arm only includes one telescopic oil cylinder, the telescopic oil cylinder includes a movable cylinder barrel 1, a cylinder head 2 is fixedly sleeved on the outer side of the cylinder barrel 1 in the longitudinal direction, two cylinder pins 3 are correspondingly arranged on both sides of the cylinder head 2, and center shafts of the two cylinder pins 3 and a center shaft of the telescopic oil cylinder are coplanar; and the telescopic oil cylinder can selectively lock or release a relative position of the telescopic oil cylinder and any telescopic arm 4 through the cylinder pins 3. In addition, arm pins 6 are arranged between adjacent telescopic arms 4 and between a basic arm 5 (a lifting arm directly pivoted with a crane upperstructure) and the first telescopic arm, and the relative positions between the adjacent telescopic arms 4 and between the basic arm 5 and the first telescopic arm can be selectively locked or released through the arm pins 6.
As shown in FIG. 1a to FIG. 1g, the extension manner of the single-cylinder plug pin type telescopic arm in the prior art is as follows: the telescopic oil cylinder can be locked with the last telescopic arm at first, and then the last telescopic arm and the second-to-last telescopic arm are released, and at this time, the telescopic oil cylinder can bring out the last telescopic arm; and after arriving at a predetermined position, the last telescopic arm is locked with the second-to-last telescopic arm again, the telescopic oil cylinder is retracted and is locked with the second-to-last telescopic arm, then the second-to-last telescopic arm and the third-to-last telescopic arm are unlocked, at this time, the telescopic oil cylinder can bring out the second-to-last telescopic arm, and after arriving at the predetermined position, the second-to-last telescopic arm is locked with the third-to-last telescopic arm again. By analogy, the telescopic arms can be extended out in turn. Of course, at any moment, any telescopic arm is either locked with other telescopic arms through the arm pins or locked with the telescopic oil cylinder through the cylinder pins.
In the existing single-cylinder plug pin type telescopic manner, the stroke of the telescopic oil cylinder is greater than the maximal stroke of each telescopic arm, and a telescopic arm can be extended from a complete retraction state to a 100% complete extension state at one time.
The single-cylinder plug pin type telescopic arm in the prior art has the following disadvantages:
1. To ensure that the oil cylinder can achieve such a large stroke and can propel the telescopic arms to extend out stably, the cylinder rod and the cylinder barrel of the oil cylinder are required to be very thick and long, meanwhile more oil is needed, and thus a hydraulic system needs to be configured with a larger oil tank to meet telescopic demands. It results in a very high cost of the oil cylinder and an overlarge weight of the crane upperstructure, indirectly increases the weight of a chassis, limits the lifting performance, approaches to the lowest requirement of the national standard and greatly affects the competitive advantage of the product.
2. The cost is high. The stroke of the telescopic oil cylinder needs to meet the extension stroke of each telescopic arm, resulting in that the stroke of the telescopic oil cylinder is too long. The cylinder rod and the cylinder barrel of a long oil cylinder are difficult to be processed, and professional and special processing equipment and processing conditions are needed, such that the cost of the telescopic oil cylinder is greatly increased.
3. The weight is large. As the telescopic oil cylinder is too long and needs to bear larger axial compression load, to prevent longitudinal bending of the telescopic oil cylinder and meet the stability requirement, larger rod diameter, cylinder diameter and material thickness of the oil cylinder are required, and a longer guide distance is required, thereby increasing the weight of the telescopic oil cylinder. Meanwhile, to meet the telescopic demand of a large-stroke oil cylinder, an oil tank with a larger size needs to be configured, and this increases the weight of the crane.
Since the weights of road vehicles are exactly regulated in the national traffic regulations, the increase of the weight causes a complex design of the crane, and the vehicle toll is increased accordingly.
4. The stability is poor. In the long-stroke telescopic oil cylinder, after the cylinder rod extends out, due to the overlarge weight per se, the connecting positions of the cylinder rod and the cylinder barrel at the middles are bent downwards, which increases the friction force of the telescopic oil cylinder. Meanwhile, due to the influence of the elastic modulus of hydraulic oil, a creeping condition occurs during the latter half of extension of the oil cylinder to cause a chattering phenomenon.